Traditionally, candles have been constructed out of solid blocks of fuel (e.g., wax) including embedded wicks which, when lit, provided light and oftentimes a measureable amount of heat. More recently, candles have been made of one or more of paraffin (a byproduct of petroleum refining), beeswax, soy, other plant waxes, and/or tallow (a by-product of beef-fat rendering). Additionally, gel candles are sometimes manufactured from a mixture of paraffin and plastic. A wide variety of devices to hold candles exist, from simple tabletop candle holders (e.g., candlesticks) up to elaborate chandeliers.
After the wick is lit (e.g., with a match or lighter), the heat from the lit wick eventually causes a small portion of the wax or other fuel of the candle to melt and vaporize. Once vaporized, the fuel combines with oxygen in the atmosphere to form a flame. This flame provides sufficient heat to keep the candle burning by way of a self-sustaining chain of events: the heat of the flame melts the top of the mass of solid fuel, the liquefied fuel then moves upward through the wick via capillary action, and the liquefied fuel is then vaporized to burn within the candle's flame.
Candles have been used for illumination since before the advent of electricity and in areas without electricity. In the developed world today, candles are used mainly for their aesthetic value and scent, particularly to set a soft, warm, or romantic ambiance, and for emergency lighting during electrical power failures. For instance, scented candles are often used in aromatherapy.
Candles are also used in the religious practices and/or ceremonies of many faiths. For instance, candles are often lit both at dawn and at dusk in many Hindu homes, and some even maintain lighting of the candles continuously between dawn and dusk. As another example, the candle is commonly used in worship both for decoration and ambiance in the Christian faith, e.g., as a symbol that represents the light of God or, specifically, the light of Jesus Christ.
However, candles are one of the leading sources of residential fires in the United States, with almost 10% of civilian injuries and 6% of civilian fatalities from fire attributed to candles. For instance, candles are oftentimes inadvertently knocked over resulting in a spillage of hot wax and/or the contact of the flame with unintended ignitable objects (e.g., drapes, carpet, etc.). Furthermore, a candle flame that is longer than its laminar smoke point often emits soot that, when inhaled, has been known to cause health hazards. Still further, allowing a candle to burn continuously results continuous melting of the wax or other fuel and the premature loss of use of the candle.